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1. Tehnology Field
The present invention relates generally to thermal transfer overcoat (xe2x80x9cTTOxe2x80x9d) technology.
2. Description of Related Art
In thermal transfer overcoat technology, a thin film is adhered to a document to provide durability and a glossy finish. A generic TTO apparatus 100 is illustrated by FIG. 1 (Prior Art). An automatic document feeder (xe2x80x9cADFxe2x80x9d) 101 as would be known in the art feeds a pre-printed document (represented by the so-labeled horizontal line) to a nip between a pressure roller 103 and a heat roller 105. An overcoat film 107 from a film supply reel 109 is threaded through the same nip. The film 107 is generally a thermally-transferable adhesive laminate material, activated by the heat roller 105, to form a clear overcoat of the printed surface of the document. After passing through the nip, a peel bar device 111 downstream of the nip separates a backing of the film 107 away from the now overcoated document 113. A film take-up reel 115 receives the film backing material.
One of the most delicate parameters to control in thermal transfer overcoat technology is the film and media interface temperature in the nip. To properly perform an overcoating operation, the adhesive coating needs to melt so that it fluidically fills the pores in the document medium, forming the overcoat finish on the final overcoated document product. Moreover, for acceptable throughput, e.g., three pages per minute (xe2x80x9cppmxe2x80x9d), the process must take place relatively quickly. Moreover, when the document being overcoated is mated to the film in the nip, a relative large heat sink develops. Commonly, temperature is monitored during the thermal transfer overcoating operation and processes are reactively controlled, namely by adding significant heat when a lowest acceptable temperature is sensed. This approach causes large temperature oscillations. It also generally requires a relatively powerful and fast-acting heat source. Generally, a reactive system must employ a more expensive product architecture, e.g., providing additional heating elements, sensors, and controls, to minimize thermal mass. Otherwise it requires a steady-state, continuous operation to achieve stability.
The present invention provides for methods and apparatus for performing an overcoat operation within a specified temperature range for optimizing output quality and throughput by anticipating overcoat operation process events.
The foregoing summary is not intended to be an inclusive list of all the aspects, objects, advantages and features nor should any limitation on the scope of the invention be implied therefrom. This Summary is provided in accordance with the mandate of 37 C.F.R. 1.73 and M.P.E.P. 608.01(d) merely to apprise the public, and more especially those interested in the particular art to which the invention relates, of the nature of the invention in order to be of assistance in aiding ready understanding of the patent in future searches.